In order to meet wireless data traffic demands that have increased after 4th Generation (4G) communication system commercialization, efforts to develop an improved 5G communication system or a pre-5G communication system have been made. For this reason, the 5G communication system or the pre-5G communication system is called a beyond 4G network communication system or a post LTE system.
In order to achieve a high data transmission rate, an implementation of the 5G communication system in a mmWave band (for example, 60 GHz band) is being considered. In the 5G communication system, technologies such as beamforming, massive Multi-Input Multi-Output (MIMO), Full Dimensional MIMO (FD-MIMO), array antenna, analog beam-forming, and large scale antenna are discussed to mitigate propagation path loss in the mmWave band and increase a propagation transmission distance.
Further, technologies such as an evolved small cell, an advanced small cell, a cloud Radio Access Network (cloud RAN), an ultra-dense network, Device to Device communication (D2D), a wireless backhaul, a moving network, cooperative communication, Coordinated Multi-Points (CoMP), and interference cancellation have been developed to improve the system network in the 5G communication system.
In addition, the 5G system has developed Advanced Coding Modulation (ACM) schemes such as Hybrid FSK and QAM Modulation (FQAM) and Sliding Window Superposition Coding (SWSC), and advanced access technologies such as Filter Bank Multi Carrier (FBMC), Non Orthogonal Multiple Access (NOMA), and Sparse Code Multiple Access (SCMA).
One of the subjects of research on next generation communication after 4G communication is to increase a system communication capacity by increasing an available frequency band. As a frequency band to be added to increase the frequency band, a method of using a carrier of a band from 3 to 30 GHz (millimeter eave band), that is, a millimeter wave carrier is considered rather than using a carrier of a frequency band below 3 GHz used in a commercial cellular system.
The millimeter wave (mmWave) carrier of the band from 3 to 30 GHz may have directivity due to propagation characteristics, and a beamforming technique may be used for controlling interference when the carrier is operated. In the millimeter wave band, not only a Base Station (BS) but also a User Equipment (UE) may generate beams having a particular angle and width through multiple array antennas to perform communication. That is, the BS and the UE may use transmission/reception beamforming to solve a path attenuation problem occurring in the millimeter wave carrier. The BS and the UE may operate a plurality of transmission/reception beamformings, and may use the plurality of transmission/reception beamformings in random access (RA) resources.
When the UE performs random access through one random transmission beam in a state where the BS forms a plurality of reception beams, the transmission beam of the UE may have links with one or more reception beams of the BS. For example, the UE may have links with a plurality of reception beams of the BS according to whether the reception beams of the BS correspond to LOS (Line Of Sight) or NLOS (Non-Line Of Sight). At this time, the UE having a link with one reception beam of the BS may be hindered in its random access by another UE having links with two or more reception beams of the BS.
FIG. 1A and FIG. 1B illustrate a concept of a random access operation of a UE in a mobile communication system.
FIG. 1A illustrates a situation where UEs are connected to a plurality of different reception beams and perform uplink random access.
A BS 120 may form a plurality of reception beams (for example, including B#1 122 and B#2 124). UE#1 100 may have links 102 and 104 with at least one of the reception beams B#1 122 and B#2 124 by using one or more transmission beams, and UE#2 110 may have a link 114 with reception beams B#2 124 by using one or more transmission beams.
FIG. 1B illustrates an RA resource set 140 that can be used by UE#1 100 and UE#2 110.
The RA resource set 140 has an RA resource structure defined by beam resources (x axis) and frequency-time resources (y axis). That is, the x axis of the RA resource set 140 corresponds to an axis of the reception beam of the BS and the y axis corresponds to an axis of frequency-time resources. For simplification, two-dimensional radio resources defined by the frequency and time are represented on the y axis in one dimension.
UE#1 100 has the links with reception beam B#1 122 and B#2 124 and thus has 10 resources in a resource area 142 by reception beam B#1 122 and B#2 124 as RA resources. In contrast, UE#2 110 has the link with reception beam B#2 124 and thus has 5 resources in a resource area 144 by reception beam B#2 124 as RA resources. At this time, UE#1 100 may select frequency-time resources R#4 146 and 148 for B#1 122 and B#2 124, and UE#2 110 and perform random access, and UE#2 110 may select only frequency-time resources R#4 146 for B#2 124 and perform random access.
When UE#1 100 and UE#2 110 simultaneously perform random access by using the frequency-time resources R#4 146 of reception beam B#2 (that is, collision occurs), UE#2 110 has no other available RA resources and thus fails in random access. However, UE#1 100 can use other available RA resources, that frequency-time resources R#4 144 of B#1 and thus has an RA success possibility.
That is, a UE having a larger number of reception beams connected thereto holds a dominant position in an RA competition. Further, a UE having a smaller number of reception beams connected thereto is at a disadvantageous position in the RA competition.
In a communication system using a millimeter wave carrier, one BS may possess a large number of RA resources (that is, transmission/reception beams) from an angle of spatial resources. That is, in the millimeter wave carrier communication system, there are a plurality of reception beams and a plurality of UEs attempt RA for the plurality of reception beams.